Some aspects of the intratubular precipitation of calcium salts

Patients who have produced one or more calcium stones are facing a consider able risk of becoming recurrent stone formers, and for those with the great est risk it is highly desirable to provide an efficient stone preventive tr eatment. Such measures, however, require a detailed understanding of the mo st important determinants of stone formation. The development of a calcium stone in the urinary tract is considered to be the result of an imbalance b etween crystallization driving, promoting, and inhibiting forces that act t ogether with a retention of the precipitated calcium crystal phases. To und erstand the formation of urinary tract calcium stones, it is essential to c onsider the fact that these stones commonly are composed of calcium oxalate as well as calcium phosphate and that the process that leads to the final stone includes precipitation of both of these crystal phases. The first ste ps of stone formation most certainly occur within the nephron, where urine is supersaturated with calcium oxalate in the collecting duct and with calc ium phosphate at higher nephron levels. After a series of crystallization e vents in the nephron, the final steps in building the stone will take place in the caliceal urine environment, the details of which are surprisingly l ittle understood, but it can be assumed that urine flow dynamics are of imp ortance for this process.